1. Technical Field
The present invention relates to methods of detecting the liquid amount, printers, and printing systems.
2. Related Art
Inkjet printers form dots on paper by ejecting ink droplets onto the paper. By forming such dots at predetermined locations on the paper, a print image constituted by numerous dots is printed on the paper. In such printers, ink is consumed by printing. When ink runs out, the user replaces ink cartridges.
As a method of detecting the amount of ink within an ink cartridge, a method of applying a drive signal to a piezoelectric element attached to the ink cartridge, detecting an output signal from the piezoelectric element due to a residual vibration after the application of the drive signal, and detecting the amount of remaining ink based on the output signal of the piezoelectric element is known (e.g., Japanese Patent Application Laid-Open Publication No. 2001-146019).
This detection method utilizes differences in resonance frequency of the residual vibration. That is to say, whether or not ink is present at a position where the piezoelectric element is attached is detected in such a manner that when the resonance frequency of the residual vibration detected by the piezoelectric element is, for example, 30 kHz, it is determined that ink is present, and when the resonance frequency is, for example, 100 kHz, it is determined that ink is not present.
However, when the piezoelectric element is driven at a resonance frequency of the residual vibration in the case where ink is present at the attaching position of the piezoelectric element, the residual vibration hardly occurs when ink is not present at the attaching position of the piezoelectric element. Moreover, when the piezoelectric element is driven at a resonance frequency of the residual vibration in the case where ink is not present at the attaching position of the piezoelectric element, the residual vibration hardly occurs when ink is present at the attaching position of the piezoelectric element. Consequently, whether or not ink is present may not be detected correctly.
Moreover, it requires two detection operations and therefore an increased detection time to first drive the piezoelectric element at a resonance frequency of the residual vibration in the case where ink is present at the attaching position of the piezoelectric element to detect the presence of ink at the attaching position of the piezoelectric element and then drive the piezoelectric element at a resonance frequency of the residual vibration in the case where ink is not present at the attaching position of the piezoelectric element to detect the absence of ink at the attaching position of the piezoelectric element.